Interest in the mechanism of spiral growth as exhibited by certain plant cell8 goes beyond a mere desire to understand what forces might cause the cellulose or chitin membrane of tl tubular cell to be a twisted rather than a straight structure. The propagation in an elongating cell wall of the twisted configuration depends on active growth of an oriented type in the primary wall. If the twist originates, as appears to be the case in the cell of Phycomyces, from an interaction between tensions in the membrane, then these tensions are exerted on the wall framework present in the growing region, and govern there the orientation of new wall substance which is being intercalated.
Recent optical studies of the plant cell wall which is growing in area have suggested the presence of a labile cellulose framework in which the structural chains are arranged in a rather disoriented crisscross mesh (Bonner, '35 ; Fney-Wyssling, '36). Yet if spiral growth and structure in the cell of Phycomyces are founded upon the elastic properties of the primary wall as has been suggested (Castle, '36 a), there must be in this growing wall a quite definite orientation of elastic properties. This paper describes measurements of the distribution of velocities of growth in length and of velocities of rotation (twist) within the growing region of the spore-bearing cell of Phycomyces, and relates this data to the theory of spiral growth and to the properties of the primary cell wall.